mirror of
https://github.com/dolthub/dolt.git
synced 2026-05-03 11:30:28 -05:00
Rafael Weinstein
106 lines
3.0 KiB
Go
106 lines
3.0 KiB
Go
package datas
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import (
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"github.com/attic-labs/noms/chunks"
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. "github.com/attic-labs/noms/dbg"
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"github.com/attic-labs/noms/ref"
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"github.com/attic-labs/noms/types"
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)
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type DataStore struct {
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chunks.ChunkStore
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rt chunks.RootTracker
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rc *rootCache
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roots RootSet
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}
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func NewDataStore(cs chunks.ChunkStore, rt chunks.RootTracker) DataStore {
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return newDataStoreInternal(cs, rt, NewRootCache(cs))
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}
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func newDataStoreInternal(cs chunks.ChunkStore, rt chunks.RootTracker, rc *rootCache) DataStore {
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return DataStore{
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cs, rt, rc, rootSetFromRef(rt.Root(), cs),
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}
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}
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func rootSetFromRef(rootRef ref.Ref, cs chunks.ChunkSource) RootSet {
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var roots RootSet
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if (rootRef == ref.Ref{}) {
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roots = NewRootSet()
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} else {
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roots = RootSetFromVal(types.MustReadValue(rootRef, cs).(types.Set))
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}
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return roots
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}
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func (ds *DataStore) Roots() RootSet {
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return ds.roots
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}
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func (ds *DataStore) Commit(newRoots RootSet) DataStore {
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Chk.True(newRoots.Len() > 0)
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// TODO: We probably shouldn't let this go *forever*. Considrer putting a limit and... I know don't...panicing?
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for !ds.doCommit(newRoots) {
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}
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return newDataStoreInternal(ds.ChunkStore, ds.rt, ds.rc)
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}
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// doCommit manages concurrent access the single logical piece of mutable state: the current root (rootSet). doCommit is optimistic in that it is attempting to create a new root making the assumption that currentRootRef is the existing root. The call to UpdateRoot below will fail if that assumption fails (e.g. because of a race with another writer) and the entire algorigthm must be tried again.
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func (ds *DataStore) doCommit(roots RootSet) bool {
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Chk.True(roots.Len() > 0)
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currentRootRef := ds.rt.Root()
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// Note: |currentRoots| may be different from |ds.roots| and *must* be consistent with |currentRootRef|.
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var currentRoots RootSet
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if currentRootRef == ds.roots.Ref() {
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currentRoots = ds.roots
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} else {
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currentRoots = rootSetFromRef(currentRootRef, ds)
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}
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newRoots := roots.Union(currentRoots)
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roots.Iter(func(root Root) (stop bool) {
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if ds.isPrexisting(root, currentRoots) {
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newRoots = newRoots.Remove(root)
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} else {
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newRoots = RootSetFromVal(newRoots.NomsValue().Subtract(root.Parents()))
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}
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return
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})
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if newRoots.Len() == 0 || newRoots.Equals(currentRoots) {
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return true
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}
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// TODO: This set will be orphaned if this UpdateRoot below fails
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newRootRef, err := types.WriteValue(newRoots.NomsValue(), ds)
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Chk.NoError(err)
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return ds.rt.UpdateRoot(newRootRef, currentRootRef)
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}
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func (ds *DataStore) isPrexisting(root Root, currentRoots RootSet) bool {
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if currentRoots.Has(root) {
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return true
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}
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// If a new root directly superceeds an existing current root, it can't have already been committed because its hash would be uncomputable.
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superceedsCurrentRoot := false
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root.Parents().Iter(func(parent types.Value) (stop bool) {
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superceedsCurrentRoot = currentRoots.Has(RootFromVal(parent))
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return superceedsCurrentRoot
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})
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if superceedsCurrentRoot {
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return false
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}
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ds.rc.Update(currentRoots)
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return ds.rc.Contains(root.Ref())
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}
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